Reflex, magnifying optical system

ABSTRACT

A first lens group in a reflex, magnifying optical system includes sequentially from the side of an object, a first lens that has a negative refractive power and is a meniscus lens having a concave aspect facing toward an image, an optical element (prism) that refracts an optical path, a second lens having a negative refractive power and a concave aspect facing toward the object, and a third lens having a positive refractive power. A portion of an image-side aspect of the first lens abuts a plane of incidence of the optical element. A portion of an object-side aspect of the second lens abuts a plane of transmission of the optical element.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a reflex, magnifying optical system.

2. Description of the Related Art

Recently, accompanying demand for smaller sized imaging devices, thereis demand for smaller sized lenses mounted on the imaging devices aswell. In response, reflex optical systems employing a prism in anoptical path to refract the optical path have been proposed, such asthose disclosed in Japanese Patent Application Laid-Open PublicationNos. 2005-128065, 2004-334070, 2004-333721, 2007-232974, and2004-163477.

Reflex optical systems disclosed in the publications achieve a reduceddepth (thickness) by refracting the light path. Consequently, mountingof these reflex optical systems has enabled imaging devices to haveshortened depths as well.

The lens arranged on the incident side or on the emission side of theprism that refracts the optical path tends to have high errorsensitivity (e.g., tilt error). High error sensitivity is undesirableand leads to significant deterioration of optical performance. Each ofthe reflex optical systems disclosed in the publications place greatemphasis on achieving reductions in the size of the optical system andin doing so, a problem arises in that the means for reducing the errorsensitivity is insufficient.

SUMMARY OF THE INVENTION

It is an object of the present invention to at least solve the aboveproblems in the conventional technologies.

A reflex, magnifying optical system according to one aspect of thepresent invention is a variable-magnification optical system that hasmultiple lens groups and varies magnification by moving any of the lensgroups. The reflex, magnifying optical system includes an opticalelement that refracts an optical path and is provided in a first lensgroup arranged closest to an object. Further, a first lens havingcurvature is disposed so as to abut a plane of incidence of the opticalelement and a second lens having curvature is disposed so as to abut aplane of transmission of the optical element.

The other objects, features, and advantages of the present invention arespecifically set forth in or will become apparent from the followingdetailed description of the invention when read in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross sectional view of a first lens group in a reflex,magnifying optical system;

FIG. 2 depicts the shape of a first lens of the first lens group;

FIG. 3 is a cross sectional view of a reflex, magnifying optical systemaccording to a first embodiment;

FIG. 4 is a diagram of spherical aberration at the wide-angle edge ofthe reflex, magnifying optical system according to the first embodiment;

FIG. 5 depicts diagrams of astigmatism and distortion at the wide-angleedge of the reflex, magnifying optical system according to the firstembodiment;

FIG. 6 is a diagram of chromatic aberration of magnification at thewide-angle edge of the reflex, magnifying optical system according tothe first embodiment;

FIG. 7 is a diagram of spherical aberration at the intermediate edge ofthe reflex, magnifying optical system according to the first embodiment;

FIG. 8 depicts diagrams of astigmatism and distortion at theintermediate edge of the reflex, magnifying optical system according tothe first embodiment;

FIG. 9 is a diagram of chromatic aberration of magnification at theintermediate edge of the reflex, magnifying optical system according tothe first embodiment;

FIG. 10 is a diagram of spherical aberration at the telephoto edge ofthe reflex, magnifying optical system according to the first embodiment;

FIG. 11 depicts diagrams of astigmatism and distortion at the telephotoedge of the reflex, magnifying optical system according to the firstembodiment;

FIG. 12 is a diagram of chromatic aberration of magnification at thetelephoto edge of the reflex, magnifying optical system according to thefirst embodiment;

FIG. 13 is a cross sectional view, along the optical axis, of a reflex,magnifying optical system according to a second embodiment;

FIG. 14 is a diagram of spherical aberration at the wide-angle edge ofthe reflex, magnifying optical system according to the secondembodiment;

FIG. 15 depicts diagrams of astigmatism and distortion at the wide-angleedge of the reflex, magnifying optical system according to the secondembodiment;

FIG. 16 is a diagram of chromatic aberration of magnification at thewide-angle edge of the reflex, magnifying optical system according tothe second embodiment;

FIG. 17 is a diagram of spherical aberration at the intermediate edge ofthe reflex, magnifying optical system according to the secondembodiment;

FIG. 18 depicts diagrams of astigmatism and distortion at theintermediate edge of the reflex, magnifying optical system according tothe second embodiment;

FIG. 19 is a diagram of chromatic aberration of magnification at theintermediate edge of the reflex, magnifying optical system according tothe second embodiment;

FIG. 20 is a diagram of spherical aberration at the telephoto edge ofthe reflex, magnifying optical system according to the secondembodiment;

FIG. 21 depicts diagrams of astigmatism and distortion at the telephotoedge of the reflex, magnifying optical system according to the secondembodiment; and

FIG. 22 is a diagram of chromatic aberration of magnification at thetelephoto edge of the reflex, magnifying optical system according to thesecond embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to the accompanying drawings, exemplary embodiments accordingto the present invention are explained in detail below.

A reflex, magnifying optical system according to embodiments of thepresent invention includes sequentially from an object side, a firstlens group having a negative refractive power, a second lens grouphaving a positive refractive power, a third lens group having a negativerefractive power, and a fourth lens group having a positive refractivepower. The reflex, magnifying optical system varies magnification bymoving the second lens group and the third lens group along an opticalaxis.

FIG. 1 is a cross sectional view, along the optical axis, of the firstlens group in the reflex, magnifying optical system. As depicted in FIG.1, the first lens group includes sequentially from the object side(object not depicted), a first lens L₁ that has a negative refractivepower and is a meniscus lens with a concave aspect facing toward animage, an optical element (prism) P that refracts an optical path, asecond lens L₂ that has a negative refractive power and a concave aspectfacing toward the object, and a third lens L₃ that has a positiverefractive power. A portion of an aspect on the image-side of the firstlens L₁ abuts a plane of incidence of the optical element P. A portionof an aspect on the object-side of the second lens L₂ abuts a plane oftransmission of the optical element P.

Thus, by a configuration in which the first lens L₁ and the second lensL₂ respectively abut the plane of incidence and the plane oftransmission of the optical element P, reduction in the size the opticalsystem, in terms of depth, can be enhanced. By causing the first lens L₁and the second lens L₂ to abut the optical element P, opticaldislocation (tilt) of the first lens L₁ and the second lens L₂ can besuppressed and deterioration of optical performance can be prevented.

An object of the present invention is to provide a compact, reflex,magnifying optical system in which the deterioration and variation ofoptical performance is prevented by reducing error sensitivity.Particularly, with respect to the first lens L₁ and the second lend L₂,which are apt to cause error sensitivity, the following conditions areset in the present invention to reduce such error sensitivity.

When an image-side radius of curvature of the lens (first lens L₁)abutting the plane of incidence of the light of the optical element P isR₂, a value of an image-side effective aperture of the lens (first lensL₁) abutting the plane of incidence of the light of the optical elementP+1.0 mm is yR₂, a center distance between the optical element P and thelens (first lens L₁) abutting the plane of incidence of the light of theoptical element P is ΔH₂, an object-side radius of curvature of the lens(second lens L₂) abutting the plane of transmission of the light of theoptical element P is R₅, a value of an object-side effective aperture ofthe lens (second lens L₂) abutting the plane of transmission of thelight of the optical element P+1.0 mm is yR₅ a center distance betweenthe optical element P and the lens (second lens L₂) abutting the planeof transmission of the light of the optical element P is ΔH₅, it ispreferable that the following conditional expressions are satisfied:yR2>ΔH₂  (1)yR₅>ΔH5  (2)

where R₂>0 and R₅<0.

By satisfying the conditional expressions (1) and (2), positionalaccuracy can be improved between the optical element P and the lenses(first lens L₁ and second lens L₂) respectively abutting the plane ofincidence and the plane of transmission of the optical element P anddeterioration of the optical performance can be curbed more effectively.

The first lens L₁ of the reflex, magnifying optical system according tothe present embodiments has an unconventional shape. FIG. 2 depicts theshape of the first lens of the first lens group as viewed from theobject side.

As depicted in FIG. 2, the first lens L₁ is shaped so that a portion ofthe perimeter is omitted. Thus, by omitting an outer portion of thefirst lens L₁, a reduction in the size of the first lens L₁ in avertical direction (a direction perpendicular to the optical axis) canbe achieved. The omitted portion is a portion through which lightrelated to focusing does not pass and is, so to speak, an unnecessaryportion. Therefore, by omitting the unnecessary portion, the problem ofghost and flare caused by light unrelated to focusing entering theoptical system can be prevented.

In the reflex, magnifying optical system according to the presentinvention, it is preferable that at least one set of cemented lensesconfigured by cementing two lenses together is arranged on the side ofthe plane of transmission of the optical element P. By cementing twolenses together, the occurrence of chromatic aberration can besuppressed. By the cementing of two lenses together, as compared with anarrangement of individual lenses, the occurrence of manufacturing errorcan be suppressed and optical performance can be maintained.

The cemented lenses arranged on the side of the plane of transmission ofthe optical element P may be three lenses cemented together, instead oftwo lenses. By cementing three lenses together, the occurrence ofvarious aberrations can be suppressed more efficiently. By the cementingof three lenses together, as compared with an arrangement of individuallenses, centering may be omitted in the manufacturing process andtherefore, simplification of the manufacturing process can befacilitated. In addition, manufacturing errors can be prevented and highoptical performance can be maintained.

In the reflex, magnifying optical system according to the presentembodiments, the second lens group may include an optical diaphragm andthree lenses. By providing the optical diaphragm in the second lensgroup, the aperture of the optical system can be made smaller andreduction of the size of the optical system can be enhanced. Byproviding three lenses in the second lens group, well-balancedcorrection can be made for spherical aberration, astigmatism, and comathat are caused by a change in the angle of view at the time of varyingthe magnification.

In the reflex, magnifying optical system according to the presentembodiments, it is preferable that the third lens group includes anegative lens having two concave aspects. By such a configuration, theouter diameter of the lens may be made smaller. In addition, it ispreferable that the negative lens making up the third lens group isformed of resin. By forming the lens of the resin, lens processing isfacilitated and therefore, manufacturing cost can be reduced. Further, alighter weight of the lens can also be achieved.

In the reflex, magnifying optical system according to the presentembodiments, it is preferable that the fourth lens group includes apositive lens that has a convex aspect facing toward the image and whoserefractive power becomes progressively weaker towards the perimeter ofthe lens. Since the fourth lens group functions as a field lens as well,such configuration is more effective. In addition, it is preferable thatthe positive lens making up the fourth lens is formed of resin. Byforming the lens of resin, lens processing is facilitated and therefore,manufacturing cost can be reduced. Further, a lighter weight of the lenscan also be achieved.

In the reflex, magnifying optical system according to the presentembodiments, it is preferable that the first lens group and the fourthlens group are fixed at all times. By such a configuration, dust can beprevented from entering the inside of the optical system and opticalperformance can be prevented from deteriorating.

As described above, the reflex, magnifying optical system according tothe present embodiments becomes a compact, reflex, magnifying opticalsystem designed to reduce error sensitivity and prevent deterioration ofoptical performance. In particular, the reflex, magnifying opticalsystem, by being configured appropriately using lenses with an asphericsurface formed thereon, can effectively correct various aberrations witha small number of lenses and is capable of achieving reductions in thesize and the weight of the optical system as well as in themanufacturing cost.

FIG. 3 is a cross sectional view, along the optical axis, of a reflex,magnifying optical system according to a first embodiment. The reflex,magnifying optical system includes sequentially from the object side(object not depicted), a first lens group G₁₁ having a negativerefractive power, a second lens group G₁₂ having a positive refractivepower, a third lens group G₁₃ having a negative refractive power, and afourth lens group G₁₄ having a positive refractive power. The reflex,magnifying optical system varies magnification by moving the second lensgroup G₁₂ and the third lens group G₁₃ along the optical axis. The firstlens group G₁₁ and the fourth lens group G₁₄ are fixed at all times. Afilter F including an IR (infrared) cut filter, a low-pass filter, acover glass, etc. is arranged between the fourth lens group G₁₄ and animage plane IMG. The filter F is provided as necessary and may beomitted if not necessary. A light receiving surface of an imaging devicesuch as a charge-coupled device (CCD) and a complementary metal oxidesemiconductor (CMOS) is provided at the image plane IMG.

The first lens group G₁₁ includes a first lens L₁₁₁ that has a negativerefractive power and is a meniscus lens having a concave aspect facingtoward the image, a prism P₁ that refracts the optical path, a secondlens L₁₁₂ having a negative refractive power and a concave aspect facingtoward the object, and a third lens L₁₁₃ having a positive refractivepower. A portion of an aspect on the image plane IMG-side of the firstlens L₁₁₁ abuts the plane of incidence of the prism P₁. An asphericsurface is formed on both faces of the first lens L₁₁₁. The first lensL₁₁₁ is shaped so that a portion of the perimeter is omitted (see FIG.2). A portion of the object-side aspect of the second lens L₁₁₂ abutsthe plane of transmission of the prism P₁. The second lens L₁₁₂ and thethird lens L₁₁₃ abut each other.

The second lens group G₁₂ includes sequentially from the object side, afirst lens L₁₂₁ having a positive refractive power, a second lens L₁₂₂having a negative refractive power, a third lens L₁₂₃ having a positiverefractive power, and an optical diaphragm STP. The first lens L₁₂₁, thesecond lens L₁₂₂, and the third lens L₁₂₃ are cemented together. Anaspheric surface is formed on the object-side aspect of the first lensL₁₂₁ and the image plane IMG-side aspect of the third lens L₁₂₃.

The third lens group G₁₃ includes a negative lens L₁₃₁ having twoconcave aspects. An aspheric surface is formed on both aspects of thenegative lens L₁₃₁. It is preferable that the negative lens L₁₃₁ isformed of resin.

The fourth lens group G₁₄ includes a positive lens L₁₄₁ that has aconvex aspect facing toward the image and whose refractive power becomesweaker progressively toward the perimeter of the lens. An asphericsurface is formed on both faces of the positive lens L₁₄₁. It ispreferable that the positive lens L₁₄₁ is formed of resin.

Various numerical data of the reflex, magnifying optical systemaccording to the first embodiment is given.

-   Total length=29.83-   Focal length=4.23 (wide-angle edge) to 7.041 (intermediate edge) to    11.72 (telephoto edge)-   F-number=3.0 (wide-angle edge) to 5.68 (telephoto edge)-   Angle of view (2ω)=70.8° (wide-angle edge) to 44.4° (intermediate    edge) to 28.80 (telephoto edge)-   Focal length of first lens group G₁₁=−7.33-   Focal length of first lens L₁₁₁ in first lens group G₁₁=−10.21-   Focal length of second lens L₁₁₂ in first lens group G₁₁=−7.37-   Focal length of third lens L₁₁₃ in first lens group G₁₁=9.65-   Focal length of second lens group G₁₂=5.68-   Focal length of first lens L₁₂₁ in second lens group G₁₂=5.66-   Focal length of second lens L₁₂₂ in second lens group G₁₂=−7.18-   Focal length of third lens L₁₂₃ in second lens group G₁₂=6.68-   Focal length of third lens group G₁₃=−4.87-   Focal length of fourth lens group G₁₄=7.50-   Image height=3-   Magnification=2.73

(Numerical Values Related to Conditional Expression (1))

-   Image-side radius of curvature (R₂) of first lens L₁₁₁-   abutting incident plane of prism P₁=5.577797-   Value (yR₂) of image-side effective aperture of first lens-   L₁₁₁ abutting incident plane of prism P₁+1.0 mm=4.62-   Center distance (ΔH₂) between prism P₁ and first lens L₁₁₁-   abutting light incident plane of prism P₁=1.75

(Numerical Values Related to Conditional Expression (2))

-   Image-side radius of curvature (R₅) of second lens L₁₁₂-   abutting transmission plane of prism P₁=−9.24-   Value (yR₅) of image-side effective aperture of second lens-   L₁₁₂ abutting transmission plane of prism P₁+1.0 mm=3.74-   Center distance (ΔH₅) between prism P₁ and second lens L₁₁₂-   abutting transmission plane of prism P₁=0.51-   r₁=14.043806 (aspheric surface)-   d₁=0.5 nd₁=1.9229 νd₁=20.88-   r₂=5.577797 (aspheric surface)-   d₂=1.75-   r₃=∞ (prism plane)-   d₃=1.48 nd₂=1.8467 νd₂=23.78-   r₄=∞ (prism plane)-   d₄=0.50702-   r₅=−9.247252-   d₅=0.4 nd₃=1.6935 νd₃=53.34-   r₆=11.754146-   d₆=1.183268 nd₄=1.9229 νd₄=20.88-   r₇=−36.665276-   d₇=7.106451 (wide-angle edge) to 3.9135 (intermediate edge) to    0.5031 (telephoto edge)-   r₈=6.062086 (aspheric surface)-   d₈=1.615897 nd₅=1.5831 νd₅=59.46-   r₉=−6.581992-   d₉=0.4 nd₆=1.9036 νd₆=31.30-   r₁₀=1084.183991-   d₁₀=1.699976 nd₇=1.5225 νd₇=62.30-   r₁₁=−3.513409 (aspheric surface)-   d₁₁=−4.00951 (wide-angle edge) to 4.0547 (intermediate edge) to    4.875 (telephoto edge)-   r₁₂=18.81701 (aspheric surface)-   d₁₂=0.4 nd₈=1.6142 νd₈=25.57-   r₁₃=2.578228 (aspheric surface)-   d₁₃=1.366645 (wide-angle edge) to 4.5144 (intermediate edge) to    7.1045 (telephoto edge)-   r₁₄=22.927718 (aspheric surface)-   d₁₄=2.1 nd₉=1.5094 νd₉=55.87-   r₁₅=−4.464141 (aspheric surface)-   d₁₅=1.888-   r₁₆=∞ (image plane)-   Conic factor (ε) and aspheric factor (A, B, C, D)

(First Plane)

-   ε=4.627,-   A=1.26×10⁻⁴, B=−2.38×10⁻⁵,-   C=3.53×10⁻⁶, D=−6.81×10⁻⁸

(Second Plane)

-   ε=1.963,-   A=−3.08×10⁻⁴, B=−6.04×10⁻⁵,-   C=3.93×10⁻⁶, D=9.49×10⁻⁸

(Eighth Plane)

-   ε=0.359,-   A=−2.82×10⁻³, B=−2.59×10⁻⁴,-   C=1.82×10⁻⁶, D=−7.92×10⁻⁶

(Eleventh Plane)

-   ε=0.988,-   A=2.45×10⁻³, B=−7.22×10⁻⁵,-   C=−1.55×10⁻⁵, D=1.19×10⁻⁶

(Twelfth Plane)

-   ε=46.737,-   A=−2.58×10⁻², B=1.25×10⁻³,-   C=4.19×10⁻⁴, D=−6.91×10⁻⁵

(Thirteenth Plane)

-   ε=0.898,-   A=−3.22×10⁻², B=1.86×10⁻³,-   C=2.82×10⁻⁴, D=−6.67×10⁻⁵

(Fourteenth Plane)

-   ε=1.000,-   A=−3.39×10⁻⁴, B=1.85×10⁻⁴,-   C=−2.59×10⁻⁵, D=5.14×10⁻⁷

(Fifteenth Plane)

-   ε=0.814,-   A=3.40×10⁻³, B=5.16×10⁻⁵,-   C=−1.66×10⁻⁵, D=3.48×10⁻⁵,

FIG. 4 is a diagram of spherical aberration at the wide-angle edge ofthe reflex, magnifying optical system according to the first embodiment.FIG. 5 depicts diagrams of astigmatism and distortion at the wide-angleedge of the reflex, magnifying optical system according to the firstembodiment. FIG. 6 is a diagram of chromatic aberration of magnificationat the wide-angle edge of the reflex, magnifying optical systemaccording to the first embodiment. FIG. 7 is a diagram of sphericalaberration at the intermediate edge of the reflex, magnifying opticalsystem according to the first embodiment. FIG. 8 depicts diagrams ofastigmatism and distortion at the intermediate edge of the reflex,magnifying optical system according to the first embodiment. FIG. 9 is adiagram of chromatic aberration of magnification at the intermediateedge of the reflex, magnifying optical system according to the firstembodiment. FIG. 10 is a diagram of spherical aberration at thetelephoto edge of the reflex, magnifying optical system according to thefirst embodiment. FIG. 11 depicts diagrams of astigmatism and distortionat the telephoto edge of the reflex, magnifying optical system accordingto the first embodiment. FIG. 12 is a diagram of chromatic aberration ofmagnification at the telephoto edge of the reflex, magnifying opticalsystem according to the first embodiment. In the drawings, d, g, and Cdenote the aberration of a wavelength corresponding to d-rays (λ=587.56nm), g-rays (λ=435.84 nm), and C-rays (λ=656.28 nm), respectively.Symbols S and M in the astigmatism diagram denote the aberration to asagittal image surface and a meridional image surface, respectively.

FIG. 13 is a cross sectional view, along the optical axis, of a reflex,magnifying optical system according to a second embodiment. The reflex,magnifying optical system includes sequentially from the object side(object not depicted) a first lens group G₂₁ having a negativerefractive power, a second lens group G₂₂ having a positive refractivepower, a third lens group G₂₃ having a negative refractive power, and afourth lens group G₂₄ having a positive refractive power. The reflex,magnifying optical system varies magnification by moving the second lensgroup G₂₂ and the third lens group G₂₃ along the optical axis. The firstlens group G₂₁ and the fourth lens group G₂₄ are fixed at all times. Afilter F including an IR cut filter, a low-pass filter, a cover glass,etc. is arranged between the fourth lens group G₂₄ and an image planeIMG. The filter F is provided as necessary and may be omitted if notnecessary. A light receiving surface of an imaging device such as a CCDand a CMOS is provided at the image plane IMG.

The first lens group G₂₁ includes sequentially from the object side, afirst lens L₂₁₁ that has a negative refractive power and is a meniscuslens having a concave aspect facing toward the image, a prism P₂ thatrefracts the optical path, a second lens L₂₁₂ having a negativerefractive power and a concave aspect facing toward the object, and athird lens L₂₁₃ having a positive refractive power. A portion of anaspect on the image plane IMG-side of the first lens L₂₁₁ abuts theplane of incidence of the prism P₂. The first lens L₂₁₁ is shaped sothat a portion of the perimeter is omitted (see FIG. 2). A portion of anaspect on the object-side of the second lens L₂₁₂ abuts the plane oftransmission of the prism P₂. The second lens L₂₁₂ and the third lensL₂₁₃ abut each other.

The second lens group G₂₂ includes sequentially from the object side, afirst lens L₂₂₁ having a positive refractive power, a second lens L₂₂₂having a negative refractive power, a third lens L₂₂₃ having a positiverefractive power, and the optical diaphragm STP. An aspheric surface isformed on both faces of the first lens L₂₂₁. The second lens L₁₂₂ andthe third lens L₁₂₃ are cemented together.

The third lens group G₂₃ includes a negative lens L₂₃₁ having twoconcave faces. An aspheric surface is formed on both faces of thenegative lens L₂₃₁. It is preferable that the negative lens L₂₃₁ isformed of the resin.

The fourth lens group G₂₄ includes a positive lens L₂₄₁, having a convexaspect facing toward the image and whose refractive power becomes weakerprogressively toward the perimeter of the lens. An aspheric surface isformed also on both faces of the positive lens L₂₄₁. It is preferablethat the positive lens L₂₄₁ is formed of the resin.

Various numerical data of the reflex, magnifying optical systemaccording to the second embodiment is given.

-   Total length=28.49-   Focal length=4.23 (wide-angle edge) to 7.02 (intermediate edge) to    11.64 (telephoto edge)-   F-number=2.68 (wide-angle edge) to 4.82 (telephoto edge)-   Angle of view (2ω)=73.2° (wide-angle edge) to 45.6° (intermediate    edge) to 28.0° (telephoto edge)-   Focal length of first lens group G₂₁=−5.59-   Focal length of first lens L₂₁₁ in first lens group G₂₁=−8.62-   Focal length of first lens L₂₁₂ in first lens group G₂₁=−6.91-   Focal length of first lens L₂₁₃ in first lens group G₂₁=9.48-   Focal length of second lens group G₂₂=6.62-   Focal length of second lens L₂₂₁ in first lens group G₂₂=6.05-   Focal length of second lens L₂₂₂ in first lens group G₂₂=−4.93-   Focal length of second lens L₂₂₃ in first lens group G₂₂=4.35-   Focal length of third lens group G₂₃=−5.48-   Focal length of fourth lens group G₂₄=9.23-   Image height=3-   Magnification=2.73

(Numerical Values Related to Conditional Expression (1))

-   Image-side radius of curvature (R₂) of first lens L₂₁₁-   abutting incident plane of prism P₂=4.48-   Value (yR₂) of image-side aperture of first lens L₂₁₁-   abutting incident plane of prism P₂+1.0 mm=4.19-   Center distance (ΔH₂) between prism P₂ and first lens L₂₁₁-   abutting incident plane of prism P₂=1.75

(Numerical Values Related to Conditional Expression (2))

-   Image-side radius of curvature (R₅) of second lens L₂₁₂-   abutting transmission plane of prism P₂=−13.2-   Value (yR₅) of image-side effective aperture of second lens-   L₂₁₂ abutting transmission plane of prism P₂+1.0 mm=3.51-   Center distance (ΔH₅) between prism P₂ and second lens L₂₁₂-   abutting light incidence plane of prism P₂=0.38-   r₁=11.0-   d₁=0.5 nd₁=1.9036 νd₁=31.3-   r₂=4.48-   d₂=1.75-   r₃=∞ (prism plane)-   d₃=4.8 nd₂=1.9036 νd₂=31.3-   r₄∞ (prism plane)-   d₄=0.383-   r₅=−13.2-   d₅=0.4 nd₃=1.6700 νd₃=47.2-   r₆=7.28-   d₆=1.35 nd₄=1.9229 νd₄=20.9-   r₇=37.5-   d₇=6.325716 (wide-angle edge) to 3.4174 (intermediate edge) to    0.5687 (telephoto edge)-   r₈=4.0675 (aspheric surface)-   d₈=1.6 nd₅=1.5891 νd₅=61.3-   r₉=−25.543 (aspheric surface)-   d₉=0.44-   r₁₀=8.24-   d₁₀=0.4 nd₆=1.9036 νd₆=31.3-   r₁₁=2.84-   d₁₁=2.11 nd₇=1.5168 νd₇=64.2-   r₁₂=−8.16 (aspheric surface)-   d₁₂=2.526259 (wide-angle edge) to 3.010011 (intermediate edge) to    4.82663 (telephoto edge)-   r₁₃=−15.052 (aspheric surface)-   d₁₃=0.4 nd₈=1.5312 νd₈=56.0-   r₁₄=3.6637 (aspheric surface)-   d₁₄=1.419317 (wide-angle edge) to 3.843989 (intermediate edge) to    4.87607 (telephoto edge)-   r₁₅=−31.729 (aspheric surface)-   d₁₅=1.6 nd₉=1.5312 νd₉=56.0-   r₁₆=−4.337 (aspheric surface)-   d₁₆=2.38-   r₁₇=∞ (image plane)-   Conic factor (ε) and aspheric factor (A, B, C, D)

(Eighth Plane)

-   ε=1.000,-   A=−1.39×10⁻³, B=7.60×10⁻⁵,-   C=−2.15×10⁻⁵, D=1.11×10⁻⁶

(Ninth Plane)

-   ε=1.000,-   A=1.19×10⁻³, B=1.19×10⁻⁴,-   C=−2.96×10⁻⁵, D=2.06×10⁻⁶

(Thirteenth Plane)

-   ε=1.000,-   A=−1.18×10⁻², B=4.70×10⁻³,-   C=−1.72×10⁻³, D=2.56×10⁻⁴

(Fourteenth Plane)

-   ε=1.000,-   A=−1.09×10⁻², B=4.91×10⁻³,-   C=−1.65×10⁻³, D=2.17×10⁻⁴

(Fifteenth Plane)

-   ε=1.000,-   A=3.38×10⁻⁴, B=−1.51×10⁻⁴,-   C=2.97×10⁻⁵, D=−6.33×10⁻⁷

(Sixteenth Plane)

-   ε=1.000,-   A=3.24×10⁻³, B=−2.70×10⁻⁴,-   C=2.19×10⁻⁵, D=5.09×10⁻⁷

FIG. 14 is a diagram of spherical aberration at the wide-angle edge ofthe reflex, magnifying optical system according to the secondembodiment. FIG. 15 depicts diagrams of astigmatism and distortion atthe wide-angle edge of the reflex, magnifying optical system accordingto the second embodiment. FIG. 16 is a diagram of chromatic aberrationof magnification at the wide-angle edge of the reflex, magnifyingoptical system according to the second embodiment. FIG. 17 is a diagramof spherical aberration at the intermediate edge of the reflex,magnifying optical system according to the second embodiment. FIG. 18depicts diagrams of astigmatism and distortion at the intermediate edgeof the reflex, magnifying optical system according to the secondembodiment. FIG. 19 is a diagram of chromatic aberration ofmagnification at the intermediate edge of the reflex, magnifying opticalsystem according to the second embodiment. FIG. 20 is a diagram ofspherical aberration at the telephoto edge of the reflex, magnifyingoptical system according to the second embodiment. FIG. 21 depictsdiagrams of astigmatism and distortion at the telephoto edge of thereflex, magnifying optical system according to the second embodiment.FIG. 22 is a diagram of chromatic aberration of magnification at thetelephoto edge of the reflex, magnifying optical system according to thesecond embodiment. In the drawings, d, g, and C denote the aberration ofa wavelength corresponding to d-rays (λ=587.56 nm), g-rays (λ=435.84nm), and C-rays (λ=656.28 nm), respectively. Symbols S and M in theastigmatism diagram denote the aberration to a sagittal image surfaceand a meridional image surface, respectively.

In the numerical data above, r₁, r₂, . . . denote the radius ofcurvature of respective lenses; d₁, d₂, . . . denote the thickness orsurface separation of respective lenses; nd₁, nd₂, . . . denote theindex of refraction of the d-rays in respective lenses; and yd₁, yd₂, .. . denote Abbe number of the d-rays in respective lenses.

Each of the aspheric shapes above is expressed by equation 1, where theX axis represents the optical axis, the Y axis represents the directionperpendicular to the optical axis, and the direction of travel of thelight is assumed as positive:

$\begin{matrix}{X = {\frac{Y^{2}/R}{1 + \sqrt{1 - {ɛ\;{Y^{2}/R^{2}}}}} + {AY}^{4} + {BY}^{6} + {CY}^{8} + {DY}^{10}}} & 1\end{matrix}$

where, R is a paraxial radius of curvature, ε is the conic factor, andA, B, C, and D are aspheric factors of fourth order, sixth order, eighthorder, and tenth order, respectively.

The reflex, magnifying optical system according to the present inventionhaving the configuration described above is a compact, reflex,magnifying optical system designed to reduce error sensitivity andprevent deterioration of optical performance.

The reflex, magnifying optical system according to the presentinvention, having a configuration in which two lens respectively abutthe plane of incidence and the plane of transmission of the opticalelement that refracts the optical path, can enhance reduction of thesize of the optical system in terms of depth, suppresses opticaldislocation (tilt) of the lenses, and prevents deterioration of opticalperformance.

The reflex, magnifying optical system according to the presentinvention, by omitting a portion of the perimeter of the lens abuttingthe optical element, can reduce a dimension of the lens in a verticaldirection (perpendicular to optical axis) and prevents a problem of thelight unrelated to focusing entering the optical system, causing ghostand flare phenomena.

By arranging the cemented lenses on the light emission side of theoptical element, the occurrence of chromatic aberration can besuppressed. Use of the cemented lenses, as compared with an arrangementof individual lenses, enables centering to be omitted in themanufacturing process and therefore, simplification of the manufacturingprocess can be enhanced. In addition, manufacturing errors can beprevented and high optical performance can be maintained.

The reflex, magnifying optical system, by being configured appropriatelyusing lenses with an aspheric surface formed thereon, can effectivelycorrect various aberrations with a small number of lenses and canachieve reductions in size and weight of the optical system, and inmanufacturing cost.

Although the invention has been described with respect to a specificembodiment for a complete and clear disclosure, the appended claims arenot to be thus limited but are to be construed as embodying allmodifications and alternative constructions that may occur to oneskilled in the art which fairly fall within the basic teaching hereinset forth.

The present document incorporates by reference the entire contents ofJapanese priority document, 2008-060149 filed in Japan on Mar. 10, 2008.

1. A reflex, magnifying optical system that is a variable-magnificationoptical system having a plurality of lens groups and varyingmagnification by moving any of the lens groups, the reflex, magnifyingoptical system comprising: an optical element that is a prism refractingan optical path, an aspect of the prism on an object-side includingstraight edges symmetrical with respect to an optical axis; a first lensthat includes planes parallel with the optical axis and symmetrical withrespect to the optical axis, and includes a concave aspect facing theobject-side of the optical element, a perimeter of the planes abuttingthe straight edges of the aspect of the optical element, and a secondlens that includes a concave aspect facing an image side of the opticalelement with a radius of the second lens being smaller than a radius ofthe image side of the optical element and abuts the image side of theoptical element.
 2. The reflex, magnifying optical system according toclaim 1, wherein the first lens has a negative refractive power and anaspheric surface on both sides, and the second lens includes two lensesabutting each other and has a negative refractive power.
 3. The reflex,magnifying optical system according to claim 2, comprising four lensgroups, wherein a first lens group consists of: the first lens; theoptical element; and the second lens, a second lens group consists ofthree lenses and has a positive refractive power, a third lens groupconsists of a single lens and has a negative refractive power, and afourth lens group consists of a single positive lens with a convexaspect facing toward an image.
 4. The reflex, magnifying optical systemaccording to claim 3, wherein at least two lenses of the second lensgroup are cemented together.